Fractionation of Hydrogen Isotopes by Sulfate- and Nitrate-Reducing Bacteria.

Hydrogen atoms from water and food are incorporated into biomass during cellular metabolism and biosynthesis, fractionating the isotopes of hydrogen-protium and deuterium-that are recorded in biomolecules. While these fractionations are often relatively constant in plants, large variations in the magnitude of fractionation are observed for many heterotrophic microbes utilizing different central metabolic pathways. The correlation between metabolism and lipid δ(2)H provides a potential basis for reconstructing environmental and ecological parameters, but the calibration dataset has thus far been limited mainly to aerobes. Here we report on the hydrogen isotopic fractionations of lipids produced by nitrate-respiring and sulfate-reducing bacteria. We observe only small differences in fractionation between oxygen- and nitrate-respiring growth conditions, with a typical pattern of variation between substrates that is broadly consistent with previously described trends. In contrast, fractionation by sulfate-reducing bacteria does not vary significantly between different substrates, even when autotrophic and heterotrophic growth conditions are compared. This result is in marked contrast to previously published observations and has significant implications for the interpretation of environmental hydrogen isotope data. We evaluate these trends in light of metabolic gene content of each strain, growth rate, and potential flux and reservoir-size effects of cellular hydrogen, but find no single variable that can account for the differences between nitrate- and sulfate-respiring bacteria. The emerging picture of bacterial hydrogen isotope fractionation is therefore more complex than the simple correspondence between δ(2)H and metabolic pathway previously understood from aerobes. Despite the complexity, the large signals and rich variability of observed lipid δ(2)H suggest much potential as an environmental recorder of metabolism

Transport Anomalies and Marginal Fermi-Liquid Effects at a Quantum Critical Point

The behavior of the conductivity and the density of states, as well as the phase relaxation time, of disordered itinerant electrons across a quantum ferromagnetic transition is discussed. It is shown that critical fluctuations lead to anomalies in the temperature and energy dependence of the conductivity and the tunneling density of states, respectively, that are stronger than the usual weak-localization anomalies in a disordered Fermi liquid. This can be used as an experimental probe of the quantum critical behavior. The energy dependence of the phase relaxation time at criticality is shown to be that of a marginal Fermi liquid.Comment: 4 pp., LaTeX, no figs., requires World Scientific style files (included), Contribution to MB1

Estimation and Analysis of Expenses of In-Lieu-Fee Projects that Mitigate Damage to Streams from Land Disturbance in North Carolina

As North Carolina’s economy has grown, the need to mitigate adverse impacts of land disturbance on aquatic ecosystems has also grown. When land disturbance adversely affects streams, a developer or the state’s Department of Transportation can satisfy mitigation requirements through payment of fees to the state’s Ecosystem Enhancement Program (EEP). EEP then manages a stream mitigation project on behalf of the responsible party. EEP has had regulatory authority to require stream mitigation for 10 years. The needs of EEP to reassess its mitigation fee and identify ways to reduce costs of the program have grown over the decade. The first objective of this study was to account for all EEP expenses of design-bid and design-bid-build projects. The second objective was to analyze the determinants of contractual expenses with a cost function. EEP has spent or committed to spend $46.34 million for 45 design-build or designbid-build projects to restore or enhance 191,374 ft. of streams. Expenses per foot have been$242.12. Given its mandate to cover expenses for stream mitigation, EEP must raise mitigation fees, especially those for urban projects, make changes to reduce project expenses, or do both. As the length of a restored or enhanced stream increases, the expenses per foot decrease. The decrease is more pronounced in undeveloped, rural areas. Thus, EEP could produce mitigation for less expense by financing fewer projects with longer reaches or by financing more projects in undeveloped, rural areas. Other states with in-lieu-fee programs for compensatory mitigation might also use these results to reduce contractual expenses.Environmental Economics and Policy,

Interoperability: A Desert Storm Case Study

McNair Paper 18, National Defense University, 1993

An Application of a Heuristic Network Algorithm to Cable Logging Layout Design

This paper describes a method for optimizing cable logging layouts using a heuristic network algorithm. A timber harvest unit layout is formulated as a network problem. Each grid cell containing timber volume to be harvested is identified as an individual entry node of the network. Mill locations or proposed timber exit locations are identified as destinations. Each origin will then be connected to one of the destinations through alternative links representing alternative cable corridors, harvesting equipment, landing locations, and truck road segments. A heuristic algorithm for network programming is used to solve the cost minimization network problem. A computerized model has been developed to implement the method. Logging feasibility and cost analysis modules are included in the model in order to evaluate the logging feasibility of alternative cable corridors and estimate yarding and transportation costs. The model was successfully applied to a harvest planning area to generate harvesting plans. This case study indicates that the planning method is best used for pre-planning since modeling assumptions with respect to tail spar availability and unconstrained road alignments may require modification of the plan before implementation

Quantifying microbial utilization of petroleum hydrocarbons in salt-marsh sediments using the ^(13)C content of bacterial rRNA

Natural remediation of oil spills is catalyzed by complex microbial consortia. Here we take a whole-community approach to investigate bacterial incorporation of petroleum hydrocarbons from a simulated oil spill. We utilized the natural difference in carbon-isotopic abundance between a salt marsh ecosystem supported by the ^(13)C-enriched C4 grass, Spartina alterniflora, and the ^(13)C-depleted composition of petroleum to monitor changes in the ^(13)C content of biomass. Magnetic-bead capture methods for the selective recovery of bacterial RNA were used to monitor the ^(13)C content of bacterial biomass during a two-week experiment. The data show that by the end of the experiment, up to 26% of bacterial biomass derived from consumption of the freshly-spilled oil. The results contrast with the inertness of a nearby relict spill, which occurred in 1969 in West Falmouth, MA. Sequences of 16S rRNA genes from our experimental samples also were consistent with previous reports suggesting the importance of {gamma}- and {delta}-Proteobacteria and Firmicutes in the remineralization of hydrocarbons. The magnetic-bead capture approach makes it possible to quantify uptake of petroleum hydrocarbons by microbes in-situ. Although employed here at the Domain level, RNA-capture procedures can be highly specific. The same strategy could be used with genus-level specificity, something which is not currently possible using the ^(13)C content of biomarker lipids

What Explains the Incidence of the Use of a Common Sediment Control on Lots with Houses Under Construction?

To analyze compliance with one aspect of the regulation of stormwater discharge, we estimate a random-utility model of the probability that a builder uses a silt fence to control sediments on a lot with a house under construction in an urbanizing county of South Carolina. The probability increases if the builder is responsible to the subdivision’s developer or if a homeowners association exists. The probability also increases as the cost to install a silt fence decreases or the number of houses under construction per built house in a subdivision increases. The results can help county officials target inspection to improve compliance.compliance with regulation, erosion and sediment control, filter fabric, management of stormwater runoff, random-utility model, silt fence, storm water pollution prevention plan, Agribusiness, Community/Rural/Urban Development, Demand and Price Analysis, Environmental Economics and Policy, Industrial Organization, Land Economics/Use, Q01, Q24, Q53, Q58,

A Method for Determining Offtracking of Multiple Unit Vehicle Combinations

The required road width around curves on forest roads is largely determined by the difference in wheel paths between the inside front tractor wheel and the inside rear trailer wheel. This difference, known as offtracking, is a function of the vehicle and road geometry. This paper presents a method for determining the offtracking of fixed and variable length multiple unit vehicle combinations travelling over forest roads. The computational method numerically integrates the differential equations which compute the path (tractrix) that the rear of a vehicle follows from a given steering curve. A unique three-point solution method is used to determine the instantaneous center of rotation for trailers in the vehicle combination. The method is shown to have good agreement with experimental data. It is suitable for use on microcomputers for single and multiple curves. A microcomputer program, OFFTRACK, was developed using this methodology